Jim Pitman has developed (and is continuing to develop, in conjunction with EJP/ECP, Chris Burdzy) a MathSciNet citation lookup tool. (MathSciNet: http://www.ams.org/mathscinet/.)
The current version of the tool works by parsing an uploaded .tex or .bbl (TeX bibliography) file, and checking the MathSciNet db using the parsed constituents.
This could be added to OJS' citation Markup Assistant as a citation checking plugin (or possibly, a matched pair of parsing/checking plugins).